Use of mixed polyamines formed by the acid-catalyzed condensation of an n-alkylaniline, 2-chloroaniline, and formaldehyde as curing agents for polyurethanes

ABSTRACT

The mixtures of polyamines formed by the acid-catalyzed condensation of an N-alkylaniline, 2-chloro-aniline, and formaldehyde in certain ratios have im-proved properties for curing polyurethanes. They are readily blended with the liquid polyurethane because they are liquid or have low solidification points. The properties of the cured polymer can be varied by selecting the proper curing agent, that is, those richer in N-alkylamiline providing softer products, or those richer in 2-chloroamiline providing harder products.

United States Patent 1 1 3,725,354 Sundholm Apr. 3, 1973 [54] USE OF MIXED POLYAMINES 3,412,071 11/1968 Sundholm ..260/75 ED BY H AC[D CATALYZED 3,012,008 12/1961 Lister .,..260/75 N 3,097,191 7/1963 France et 81 ..260/77.5 3,277,173 10/1966 Powers et a1. ..260/570 ALKYLANILINE Z-CHLOROANILINE 3,297,758 l/1967 Hoeschele ..260/570 AND FORMALDEHYDE AS CURING 3,408,301 10/1968 Sundholm ..252/l82 AGENTS FOR POLYURETHANES Norman K. Sundholm, Middlebury, Conn.

Inventor:

Related US. Application Data Division of Ser. No. 796,549, Feb. 4, 1969, abandoned.

, US. Cl ..260/75 NH, 252/182, 260/77.5 AM,

260/570 D Int. Cl. ..C08g 22/16 Field of Search ..260/75 NH, 77.5 AM

References Cited UNITED STATES PATENTS Sundholm ..260/75 Primary ExaminerM. .1. Welsh Assistant ExaminerH. S. Cockeram AttorneyJames J. Long [57] ABSTRACT The mixtures of polyamines formed by the acid-cater lyzed condensation of an N-alkylaniline, 2-chloroaniline, and formaldehyde in certain ratios have improved properties for curing polyurethanes. They are readily blended with the liquid polyurethane because they are liquid or have low solidification points.

The properties of the cured polymer can be varied by selecting the proper curing agent, that is, those richer in N-alkylamiline providing softer products, or those richer in 2-chloroamiline providing harder products.

5 Claims, No Drawings USE OF MIXED POLYAMINES FORMED BY THE AClD-CATALYZED CONDENSATION OF AN N- ALKYLANILINE, Z-CHLOROANILINE, AND FORMALDEHYDE AS CURING AGENTS FOR POLYURETHANES This application is a division of my copending application Ser. No. 796,549, filed Feb. 4, 1969, now abandoned.

The use of 4,4'-methylenebis(2-chloroaniline), called MOCA, as a curing agent for polyurethanes is well known, but unfortunately this substance is high melting and involves certain processing disadvantages.

Mixed diamine curing agents for polyurethanes are known, as disclosed for example in U.S. Pat. No. 3,194,793 issued to Kogon (assigned to du Pont) on July 13, 1965, which shows mixtures of at least one aromatic primary diamine and at least one aromatic secondary diamine whose secondary amino groups have one valence of each nitrogen atom attached to an aromatic ring and another valence attached to an aliphatic carbon atom. My compositions are also mixtures of two such diamines along with a diamine in which one amino group is primary and the other secondary. It is due to the presence of this novel mixed primary-secondary diamine that my products have superior physical properties.

U. S. Pat. No. 3,285,879 issued to Larson and Hayes (assigned to Universal Oil Products) on Nov. 15, 1966 discloses N-monoalkyl-aromatic diamines as curing agents for polyurethanes. These give soft cured stocks which are of value for certain applications: matting, safety cushioning, etc. My compositions give hard or soft cured stocks depending on the ratio of reactants from which they are made.

My U. S. Pat. No. 3,412,071, issued Nov. 19, 1968, discloses mixed diamine curing agents for polyurethanes formed by acid-catalyzed condensation of aniline, 2-chloroaniline, and formaldehyde. The present products differ from these in that an N-alkylaniline is used in making the present products in place of aniline. The present products tend to have lower melting points and solidification points; many of them are liquids. They also provide longer pot lives when blended into a polyurethane prepolymer.

The invention is based on the discovery that certain mixtures of an N-alkylaniline and 2-chloroaniline may be reacted with formaldehyde in the presence of an acid to provide mixtures of polyamines which are effective curing agents for polyurethanes and which display unexpected and valuable properties. Many of them are liquid; those which are not liquid have melting points lower than that of 4,4-methylenebis-(2-chloroaniline) and show excellent supercooling properties.

As is well known, one means for curing polyurethanes is by the use of aromatic diamines. Generally in this method the diamine is added as a liquid to the liquid polyurethane to facilitate the blending operation. So that high temperatures are not necessary in this operation, it is advantageous that the diamine is a liquid, a low-melting solid, or a solid which when melted exhibits good super-cooling properties. lf the diamine solidifies before it is completely blended into the polymer or crystallizes from the blend, an improper cure will be obtained.

There has been a need for a diamine which has a lower melting point (lower solidification point) than that of the favored curing agent, 4,4-methylenebis-(2- chloroaniline). Commercial samples of this diamine melt in the range 99l09C. The present condensation products fulfill this need.

As indicated, the invention is concerned with curing of polyurethanes, particularly isocyanate-terminated polyurethanes. Such polyurethanes are usually prepared by reacting an excess of an organic diisocyanate with a long-chain glycol. Generally the glycols used are polyether glycols or polyester glycols. The molar ratio of diisocyanate to glycol should be greater than one and is preferably large enough so that the polyurethane is liquid. Such polyurethanes are generally called prepolymers.

Curing agents for these prepolymers are compounds which contain more than one active hydrogen-contain ing group capable of adding to the isocyanate group. Glycols and diamines are such compounds. The plurality of the addition reactions results in chain extension. When a diamine is used as the curing agent chain extension is effected through formation of substituted urea linkages. By use of a deficiency of diamine, isocyanate groups remain. These react at curing temperature with active hydrogen-containing groups, e.g., urea and urethane groups, in the polymer chain to give branch points, biuret and allophanate linkages, respectively, which result in crosslinks. When a glycol is used as the curing agent, only urethane and allophanate groups are formed. See pp. 301-6, Polyurethanes: Chemistry and Technology. Part ll. Technology by J. H. Saunders and K. C. Frisch, lnterseience Publishers, 1964, for a description of the chemical reactions involved in the curing action.

The diamines are preferred over the glycols as curing agents since they react faster and thus have shorter cure times, and generally give better properties, such as higher tensile strength and higher hardness, after curing. Aromatic diamines are the most common, since most aliphatic diamines react too fast. A favored curing agent of this type is 4,4-methylene-bis-(2- chloroaniline).

It is advantageous that the temperature of mixing of the diamine curing agent with the polyurethane is as low as possible, so the pot life of the mixture is as long as possible and the properties of the polymer are not affected. in commercial practice the diamine is usually mixed as a liquid with the liquid polyurethane so as to have quick, complete, and facile mixing. If the diamine is a solid, it is melted before mixing; the lower the solidification point, the lower the mixing temperature that can be used. The ideal diamine is one which is a liquid at ambient temperature.

There are some applications for which the conventionally used 4,4-methylenebis-(2-chloroaniline) melts high. The melted material has to be kept at an undesirably high temperature to remain liquid for extended periods, and when added to the polyurethane, which is at a lower temperature, tends to solidify before it is completely blended into the polymer or to crystallize from the blend. Such premature solidification of the diamine results in polymer-diamine mixes which do not cure properly.

The present invention is based on the discovery that certain mixtures of an N-alkylaniline and 2- ehloroaniline may be reacted with formaldehyde in the presence of an acid to provide new and useful compositions which are effective curing agents for polyurethanes. The new compositions display unexpected and valuable properties, in comparison to heretofore available diamine curing agents. Many of them are liquid; those which are not liquid have melting points lower than that of 4,4'-methylenebis(Z-chloroaniline) and show excellent supercooling properties. When a solid composition of the invention is heated to a temperature at which it is liquid, it can thereafter be cooled to a temperature much lower than the temperature at which it was melted, without tending to resolidify readily. These properties permit the ready blending of the curing agents of this invention with a polyurethane without excessively heating the blend to prevent solidification of the curing agent. Of the products of this invention prepared the highest solidification temperature is 62C. Commercial samples of the conventional 4,4-methylenebis(2-chloroaniline), in contrast, resolidify in the range 8599 C.; they melt in the range 99l 09C.

Another outstanding advantage of the new curing agents is that they have longer pot lives than 4,4- methylenebis-(2-chloroaniline). The pot life is dependent upon the N-alkylaniline used and also on the ratio of reactants. The lower the processing temperature, the longer the pot life; because the curing agents of this invention permit lower processing temperatures, blends of them with a polyurethane may exhibit even longer pot lives. Because the present curing agents are liquid or have low solidification points there is no or less likelihood that they will solidify in and plug up the lines carrying them to the mixer.

Another advantage of the new curing agents is that using the same polyurethane the properties of the cured polymer can be varied by selecting the proper curing agent. For example, softer cured stocks can be obtained by using curing agents produced from mixtures of N-alkylaniline and 2-chloroaniline increasingly richer in N-alkylaniline.

The preferred compositions having useful curing activity and either being liquid or showing good supercooling properties are those prepared by condensing formaldehyde, or formaldehyde-generating reagent, in the presence of an acid with mixtures of an N-alkylaniline and 2-chloroaniline in which the molar ratio of N-alkylaniline to 2-chloroaniline is in the range 3:1 to 1:9. Condensation products from mixtures richer in N-alkylaniline do not have good curing activity while products from mixtures richer in 2-chloroaniline have solidification points approaching that of 4,4- methylenebis-(Z-chloroaniline).

The N-alkyl group, R in 1 and ll, of the N-alkylaniline used to prepare these compositions is a primary or secondary alkyl group having one to eight carbon atoms. Illustrative examples are methyl, ethyl, npropyl, isopropyl, n-butyl, isobutyl, sec-butyl, n-hexyl, and 2-octyl.

The amount of formaldehyde, or formaldehydegenerating reagent, used should be such that the molar ratio of the sum of the two amines to formaldehyde is at least about 1.521, that is, about 1.521 or higher (e.g.,

4:1, 5:1, 10:1, or more). Any unreacted monoamines are removed from the condensation products by vacuum or steam distillation.

The condensations are carried out in inert solvents. Water is preferred, but organic solvents such as the lower alcohols (e.g., methanol, ethanol, and isopropanol) are also suitable, as well as ethers, lower aliphatic acids, aromatic hydrocarbons, etc.

The condensation is promoted by acids; it is preferred to use one of the strong mineral acids such as hydrochloric or sulfuric, but other inorganic or organic acids may be used, such as phosphoric, p-toluenesulfonic, oxalic, dichloroacetic, and trichloroacetic. It is preferred to use about one equivalent of acid per mole of total amines; however, this is not necessary. The useful amounts of acid are usually in the range from 0.5 to 2 equivalents per mole of total amines, but 0.1 to 10 equivalents may be used.

The condensations are best carried out at moderately increased temperatures; the preferred temperature range is 50l00C., although lower and higher temperatures may be used (e.g., 20150C.).

Some of the compositions have been examined by gas-liquid chromatography, which shows the presence of three characterized components, 4,4-methylenebis- (N-alkylaniline) (l), 2-chloro-N-alkyl-4,4- methylenedianiline (II), and 4,4-methylenebis-(2- chloroaniline) (III). The presence of I RNll 4 112 --Nnlt 1tNl1- 431:

EXAMPLE 1 The preparation of one of the curing agents of this invention, in which the N-alkylaniline used is N- isopropylaniline and the molar ratio of it to 2- chloroaniline is 2:1 and the molar ratio of their sum to formaldehyde is 4:1 is given as an example:

To a stirred solution of 90.0 grams (0.67 mole) of N- isopropylaniline, 42.5 grams (0.33 mole) of 2- chloroaniline, and 83.3 ml. (1.0 mole) of concentrated hydrochloric acid in 250 ml. of water at 60C. was added 20.3 grams (0.25 mole) of 37 percent formaldehyde during 45 minutes. The stirred solution was then heated at 60C. for 4 hours; grams of 28-30 percent ammonia was added and the organic layer separated and subjected to steam distillation to remove excess monoamines. The organic residue was washed with hot water and dried under reduced pressure in a rotary evaporator on a steam bath to give 56.0 grams of brown oil. This oil showed no signs of crystallization, even after seeding with 4,4-methylenebis-(2- chloroaniline) and standing for one year.

a liquid isocyanate-terminated polyurethane prepolymer prepared by adding 351.2 grams of 2,4- tolylene diisocyanate to 1,000 grams of po1y(oxytetramethylene) glycol (number-average molecular Examination of this product by vacuum distillation 5 weight 1,000) agitated at 40C. and protected from atand gas-liquid chromatography showed it to consist of mospheric moisture. The mixture was then heated at approximately 8 percent 4,4-methylenebis-(N- 80C. for 2 hours. The prepolymer obtained had an isopropylaniline), 32 percent 2-chloro-N'-isopropylequivalent weight of 660. 4,4'-methylenedianiline, 37 percent 4,4-methylenebis- A series of curing agents of the invention was (2-chloroani1ine), and 23 percent of mixed higher 10 prepared, using the procedure of Example 1, and empolyamines. ploying, as shown in Table 1, various N-alkylanilines,

I various molar ratios of N-alkylaniline to 2- 37 99 the 'N chloroaniline, A:C, and various molar ratios of total methy, ene l m these 9 amines to formaldehyde, (A C):H CO. Table I also establlshe d by isolation and characterization in one ingives the melting (clearing) point, solidification f Flfteen grams of the ll obtdmed by perature, and chlorine content. The equivalent weight densmg mole of N'methylamlme 1 mole (weight containing 1 mole of amino groups) ofthe mixchloroamlme and mole of formaldehyde. m the ture of polyamines is calculated from its chlorine conpresence of 2 moles of hydrochloric acid was dissolved tent using the expression in 50 ml. of chloroform. This solution was chromatog' 2O raphed on an alumina column using chloroform as 1 11 I1 :l eluant liquid. Sixteen l-ml. fractions were collected n) TABLE 1 Split .\111l;1r b'olitlili- 1'111 11-211 .\lol:1r l'ttlin .\11*lti11 lilllllll ('hlurinv 1111 at 'lt-nsilu l'llnngzi- 3110 "l1\l ratio tAl-t'): point, point. analysis. 1111)" t'., slrvngth, ti1111. modulus, It 1711 Alkyl group A:( ll tjt) "(X1 n J perm-111 111111. psi. llllttlli 1.. .i. 11.1.1 Methyl... 1111 -1;t .15 11; a :Lm in 1'. r1 11x11 311) 1,11111) 711 D 1:3 1.1 75 3s 21L us 1: 11,1111 3511 5.21111 70 1111. 1:1 1;1 75 J5 ism 1H axon 3711 3. .1311 5 1 I111 2n 1:] 1111 1s;- 2-, .111) :4111 1,011] 011 1).). 11:1 11:1 ()11 17.13 3,7111) 3121] Llllll 5O 11 lropyl 1:1 1:1 (111 11.011 17 1,131) (1611 l,tl. ll 1) |1-llex vl.. 111 111 nil 1.111 15 2, 71111 1311 311 )t11yl.. 111 111 7s 2s 11.2111 2:1 1x11 21m 1,5911 r111 '1,'l-Itlt11llyl1'll1|11MZ-tllltll'tmllilll1(1) tot-111111111 1111 11111 \1'. .1 1 1; 11,2110 3711 1.11m) 1111 'll1isis1.111:111111111 1111.1111:at,whichll1u1111-l11-l1-ars. h M W 7 7w '-\\'itl1:11:it:1tim1 11y SttlulJ'lllllL'.

and the chloroform evaporated. On the basis of their 40 in which E, is the equivalent weight of the 4,4- infrared spectra, the first three fractions were prinmethylene-bis(N-alkylaniline) constituent and P is the cipally 4,4'-methylenebis-(N-methylaniline); the percent chlorine. fourth through the ninth fractions showed typical To evaluate the curing agents, they are weighed out mixed primary amine-secondary amine infrared abin quantities to provide 0.9 equivalent of amine per isosorption; the thirteenth through the sixteenth fractions, cyanate equivalent using 100 grams of prepolymer. For on the basis of melting points and infrared spectra, exampl the Condensation Product p ep ed using a were 4,4-methylenebis-(2-chloroaniline). The fourth 2:1 molar ratio of N-isopropylaniline to 2-chloroaniline through the ninth fractions were combined and rechroand a 41 mo a ratio Of the sum of the two amines to matographed twice. The fractions having identical inform l hyde h a Chlorine Content of 15.82 percent frayed e tra r ombi d to i 2,0 grams of a and a calculated equivalent weight of 136; 18.5 grams oil having a boiling point of 216-218C. (2.0 m of this product is used to cure 100 grams of the The elemental analysis and infrared spectrum confirm prepolymer. The Curing agents are heated to 100C. it to be 2-chloro-N'-methyl-4,4'-methylenedianiline, and blended with the prepolymer also heated to 100C.

Calculated for C H CIN C, 68.16; H, 6.09; CI, After centrifuging for one minute, 80 grams of the 14.40; N, 11.36. Found: C, 68.44; H, 6.28; Cl, 14.59; blend is poured into a mold 7 X 7 X 0.075 inches and N, 11.14. press-cured at 100C. for one hour. The cured sheets The presence of this liquid component contributes to are removed and post-cured for 16 hours at 70C. The the good supercooling or liquid properties of the comremainder of the blend is kept in an oven at 100C. and positions prepared using N-methylaniline as the N-althe elapsed time from mixing until the blend becomes k |ani1in The presence f th 2- hl ro-N ]k 1-4,4 unpourable observed; this is the pot life. Physical promethylenedianilines in the other compositions, then, perties of the cured elastomeric sheets are determined; plays a role in determining their supercooling or liquid these are shown in Table l. The properties of the stock properties. cured with 4,4'-methylenebis(2-chloroaniline) are also given.

EXAMPLE II This example illustrates the manner of use of the mixed polyamines of the invention as curing agents for The data in Table I show that all of the compositions of the invention are either liquid, or have melting (clearing) points and solidification points lower than that of technical 4,4'-mcthylcncbis-(2 chloroanilinc). They also have pot lives longer than that of this com monly used polyurethane curing agent. The data also show that there is in general a progressive change in the properties of the polyurethane cured with compositions of this invention derived from the same N-alkylaniline; keeping the molar ratio of the sum of the two amines to formaldehyde constant, the property is dependent upon the molar ratio of N-alkylaniline to 2- chloroaniline used. This is demonstrated in the series in which N-methylaniline is used as the N-alkylaniline: as the A:C molar ratio is increased, using an (A+C): H CO molar ratio of 4:1, the tensile strength, 300 percent modulus, hardness, and tear strength decrease. Advantage can be taken of this observation; using the same polyurethane, cured properties can be varied as desired by the choice of the proper curing agents of this invention. This is of unusual value when one considers the range of practical applications in which polyurethanes are currently used, these applications being dependent upon some specified property, such as hardness.

U. S. Pat. No. 3,194,793 discloses as a polyether polyurethane curing agent a mixture of l at least one aromatic primary diamine, and (2) at least one aromatic secondary diamine whose secondary amino groups have one valence of each nitrogen atom attached to an aromatic ring and another valence attached to an aliphatic carbon atom, the molar ratio of (l) to (2) ranging from about 0.33:1 to 5.7:1; a composition of the disclosure is an equimolar mixture of 4,4-methylenebis-(2-chloroaniline) and 4,4- methylenebis-(N-methylaniline). This mixture has been prepared and compared with the composition of the present invention prepared by reacting 1 mole of formaldehyde with 2 moles of N-methylaniline and 2 moles of 2-chloroaniline in the presence of 4 moles of hydrochloric acid. As curing agents for polyurethanes tested according to the procedure of Example 11 these compositions gave about the same properties and had the same pot life at 100C. However, the composition of this invention has advantages in physical properties. It has a lower melting point, 48C. against 81C. Many days are required at 25C. for it to partially solidify, while the mixture of the prior art solidifies quite rapidly at 40C. Thus there is much less likelihood of my composition solidifying during processing.

It will be understood that the invention is applicable to the curing of conventional polyurethane prepolymers in general. As is well known to those skilled in the art such materials are produced from an organic compound rich in hydroxy groups, usually a polymer having at least two terminal hydroxy groups, frequently a polyether or polyester, and an organic polyisocyanate, usually a diisocyanate. The polymer used for reaction with the polyisocyanate to make the polyurethane is frequently a polyether or polyester glycol having a molecular weight of from 400 to 6,000, preferably in the 1,0002,000 range. Mention may be made of chain extended polyesters made from a glycol (e.g., ethylene and/or propylene glycol) and a saturated dicarboxylic acid (e.g., adipic acid). Usually the starting glycol contains from two to 20 carbon atoms and the acid contains from four to 12 carbon atoms. Poly(ethylene adipate), poly(ethylene adipate-phthalate), poly(ncopentyl sebacatc), etc, may be mentioned. Small amounts of triols such as trimcthylolpropane or trimethylolcthanc may be included. Examples of polyether glycols are p0ly(oxypropylene) glycol, poly(oxypropylene-oxyethylene) glycol, and poly(oxytetramethylene) glycol. Among the suitable polyisocyanates may be mentioned 2, 4-tolylene diisocyanate, /20 and 65/35 mixtures of 2,4- and 2,6- tolylene diisocyanates, 4,4-diphenylmethane diisocyanate, 4,4-biphenyl diisocyanate, 3,3'-dimethyl (or dimethoxy )-4,4-biphenyl diisocyanate, 1,5- naphthalene diisocyanate, mand p-phenylene diisocyanates, 1,6-hexamethylene diisocyanate, etc. The isocyanate is of course used in amount at least equivalent to the hydroxy groups in the starting polymer; larger quantities of diisocyanate favor formation of liquid prepolymer. Generally the molar ratio of diisocyanate to glycol is in the 12:1 to 3:1 range. For additional examples of suitable starting materials for making polyurethanes, reference may be had to the following: Otto Bayer in Angewandte Chemie, A59, 257

(1947) and US. Pat. No. 3,105,062, Graham and Gregg, Sept. 24, 1963. It will be understood that the present compositions may be used in the same proportions and under the same curing conditions as conventional diamine curing agents. Almost invariably the proportions of curing agent to prepolymer are such as to provide from about 0.5 to about 1.1 equivalents of amine per isocyanate equivalent in the prepolymer. The curing agent in the molten state is blended with the liquid prepolymer and is then shaped, for example, cast, molded, spread on cloth or otherwise used to coat and/or impregnate. While in the desired shape the mixture is heated to expedite cure, for example, to a temperature of 50250C. for r-48 hours (time and temperature of cure being generally inversely related) depending on such factors as the particular prepolymer used, the amount of curing agent, the degree of cure desired, the size of the article, the character of the heating device, etc. It will be understood that the curing conditions are not critical, but simply follow conventional practice. The curing agent may be employed according to the so-called green stock technique, for example, by mixing the curing agent and polyurethane and partially reacting them to a gelled, but incompletely cured, stage; the resulting solid gum (green stock) can subsequently be molded in a desired shape and cured at elevated temperature to a thermoset, crosslinked state. Useful articles of all sorts, such as gears, wheels, drive belts, conveyor belts, printing rollers, bearings, pump stators and impellers, heel lifts, gaskets, seals and electric cable jacketing, may be made using the curing agents of the invention.

Having thus described my invention what I claim and desire to protect by Letters Patent is:

1. The composition obtained by heating at curing temperature the blend of an isocyanate-terminated polyurethane prepolymer with a mixture of polyamines formed by the condensation in an inert solvent at a temperature of from 20 to C. in the presence of an acid of formaldehyde with a mixture of an N-alkylaniline and 2-chloroaniline in which the molar ratio of N-alkyl-aniline to 2-chloroaniline is in the range 3:1 to 1:9, the molar ratio of the sum of the two amines to formaldehyde is at least about 15:1, and the amount of 3. A composition as in claim 1 in which the N-alkylaniline is N-et-hylaniline 4. A composition as in claim 1 in which the N-alkylaniline is N-isopropylaniline.

5. A composition as in claim 1 in which the said curing temperature is from 50 to 250C, maintained for k to 48 hours. 

2. A composition as in claim 1 in which the N-alkylaniline is N-methylaniline.
 3. A composition as in claim 1 in which the N-alkylaniline is N-ethylaniline.
 4. A composition as in claim 1 in which the N-alkylaniline is N-isopropylaniline.
 5. A composition as in claim 1 in which the said curing temperature is from 50* to 250*C., maintained for 1/2 to 48 hours. 